This invention relates to fluid compressors and more particularly to a combined pressure equalizer and over-pressure control for use with fluid compressors.
Refrigeration units employing fluid compressors typify applications in which there exists a substantial pressure differential across the compressor following shutdown and normally for a number of hours thereafter. If it is desired to restart the compressor during the period of time when the pressure differential exists, the compressor motor must not only have sufficient torque to overcome the inherent inertia of the compressor parts, but it must also overcome the pressure differential in order to restart the compressor. The foregoing necessitates the utilization of either oversized motors or relatively expensive starting accessories.
In U.S. Pat. No. 3,398,551, assigned to the assignee of the instant invention, there is disclosed a compressor control which functions to rapidly equalize the pressure between the suction and discharge sides of the compressor to thereby eliminate the necessity for having starting accessories or the need for using oversized motors. In addition, the control disclosed in the aforecited patent operates to protect the fluid compressor during overpressure conditions.
Although the device disclosed in the aforementioned patent has proven to be extremely satisfactory from a functional standpoint, it has been found that certain of the parts of such control wear more rapidly than desired. In addition, equalization between the discharge and suction side of the compressor is not accomplished quite as rapidly as desired due to internal friction produced by the relative motion of the parts and in particular due to the utilization of an "O" ring for sealing purposes.